Retinal ischemia has been implicated in a number of retinal disorders. One category of molecules that can regulate the retina's response to ischemia is neuropeptides. An ischemia-induced increase in neuropeptide expression has been considered an endogenous protective mechanism in the retina. It is poorly understood, however, why ischemic retinal injury still occurs regardless of an increased expression in protective neuropeptides. Neuropeptides are initially synthesized as large precursors that are processed into smaller, active forms by the action of a set of processing enzymes. Our parallel studies on ischemic brains have revealed that brain ischemia has an adverse effect on the biosynthetic activation steps of key neuropeptide processing enzymes, resulting in an accumulation of neuropeptide precursors in ischemic brains. Animals null of a neuropeptide processing enzyme are more sensitive to ischemic stress. These findings have directed us to investigate if a similar, ischemia-induced blockade in neuropeptide processing may also occur in the retina, and if this may be a mechanism of ischemic retinal injury. Results of our preliminary studies on retina ganglion cells (RGC) support such notions. Little is known about the molecular mechanisms of neuropeptide processing in the retina. The specific aims of this proposal are: 1) To establish the potential involvement of proprotein converse 1 and 2 (PC1 and PC2, respectively) in retinal neuropeptide processing. These two critical enzymes process many neuropeptides in the brain including those that are also found in the retina. Studies under this aim include examination of the presence and developmental changes of PC1 and PC2 in the retina; characterization of biosynthetic activation steps of PC1 and PC2 in RGC and their potential roles in neuropeptide processing; and a quantitative proteomic comparison of neuropeptide profiles in the retinas of wild type, PC1-null and PC2-null mice. 2) To investigate how retinal ischemia may alter the activation steps of PC1 and PC2 and the production of neuropeptides by retinal cells, using both in vivo and in vitro ischemia models. The response of PC1-null and PC2-null mice to retina ischemia will also be investigated. Our long-term goal is to obtain a thorough understanding of neuropeptide processing in the retina and its role in regulating the retina's response to injurious stresses. Ultimately, such knowledge will help development of new therapeutic strategies and targets for treatment of retinal diseases. [unreadable] [unreadable] [unreadable]